1. Field of the Invention
The present invention relates to electro-optical testing. More specifically, the present invention relates to methods and apparatus for evaluating focal plane arrays using an infrared blackbody source.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art
A focal plane array senses infrared (IR) radiation and converts the received IR radiation to electrical signals. The electrical signals are processed and transmitted to another subsystem where the information is utilized. As the focal plane array will be utilized in diverse ambient temperature emvironments, the focal plane array should be tested and evaluated over the temperature range of interest.
The evaluation of a focal plane array requires a uniform blackbody source of IR radiation. A blackbody is a uniform emitter of radiation generally used to test and evaluate an IR device such as a focal plane array. Typically, a dewar is employed during the process. A dewar is an evacuated chamber void of atmospheric gases which is commonly used in cryogenic testing of semi-conductor devices such as a focal plane array. Previously, the dewar typically housed the focal plane array under test and cooperated with a blackbody radiation source external to the dewar. The IR radiation emitted from the blackbody source was then transmitted to the focal plane array within the dewar through an IR transmissive window comprised of, for example, sapphire.
To accurately characterize the performance of a focal plane array, the IR blackbody source should simulate typical terrestrial background radiation levels. The typical terrestrial background radiation levels span the range of from -40.degree. C. to +80.degree. C. Thus, the blackbody source should serve as a heat generator and provide varying intensity levels of photons that simulate the various terrestrial conditions in the laboratory. The various terrestrial conditions include the ambient air and ground temperatures of the surrounding environment.
Unfortunately, an IR blackbody source capable of simulating the temperature range of interest (e.g., from -40.degree. C. to +80.degree. C.) is not available. As a result, the focal plane array cannot be accurately characterized under all expected operating conditions without significantly reconfiguring the test dewar. In order to reconfigure the test dewar, the testing of the focal plane array must be terminated and the dewar must be opened to permit component parts to be modified. Thereafter, the testing must be reinitiated with a new set of variables. Thus, reconfiguring the test dewar is time consuming and labor intensive.
More recently developed IR blackbody sources are capable of simulating wider temperature ranges (e.g., -15.degree. C. to +50.degree. C.). However, operation of these sources results in atmospheric condensation (frost) at 0.degree. C. and below and other atmospheric effects such as air currents. These conditions substantially inhibit control of the uniformity of the IR blackbody source and thus, the test results are often inaccurate.
It is also important that the IR blackbody source be uniform in order to maintain the relationship between the blackbody source and the focal plane array. The blackbody source must be controlled and calibrated over the entire temperature range of interest to receive valid test results. However, conventional blackbody sources generally generate and transmit non-uniform levels of IR radiation.
Thus, there is a need in the art for improvements in evacuated chambers for testing semi-conductor devices to simulate typical terrestrial background radiation levels, position the blackbody radiation source proximate to the test dewar, and eliminate derogatory effects on the test results due to the atmosphere.